What condition does an operator have the least amount of control over?

An operator has the least amount of control over temperature. In wastewater treatment processes, temperature can be influenced by various external factors such as seasonal changes, weather conditions, and geographic location. While an operator may take steps to manage temperature within a treatment facility—such as using heated buildings in colder climates or controlling water input—the overall ambient temperature is largely beyond an operator's direct control.

In contrast, flow rates, wasting rates, and the food-to-microorganism (F/M) ratio can be adjusted by the operator through operational decisions and management strategies. These variables are actively managed to ensure optimal conditions for biological treatment processes, making them more manageable compared to temperature fluctuations.